The single transferable vote gives freedom of choice to electors and ensures, as far as possible, that their preference is satisfied and not distorted or frustrated.
Voters indicate their preferences for candidates by ranking them (1st choice, 2nd choice, etc.). A voter’s alternate rankings can be thought of as backup or contingency choices to make sure a member’s vote isn’t wasted on a sure winner who has a surplus of votes, or a sure loser, who can’t possibly win.
Initially, only the voter’s first choice is counted. Only if that first-choice candidate has more than enough votes to win, or if that candidate has so little support that he or she can’t win, will a ballot count towards the election of a lower preference.
The details are spelled out in Article 15, Section 1 of the Pacifica Bylaws, as summarized:
1. First a ‘winning threshold’ is calculated as:
[(the total number of valid ballots cast) ÷ (1 + the number of seats to be filled)] + 1
This is the minimum number of votes a candidate needs to get elected. Any candidates who have enough first choice votes to reach the winning threshold are declared elected.
2. If a candidate receives more votes than needed to win a seat, the “surplus” portion of each vote in a winning candidate’s pile is transferred to each of those voters’ next preference candidate so that each vote is fully used.
3. If there are still unfilled places after the first preferences have been dealt with and any surpluses transferred, then the candidate with the lowest number of votes is eliminated and voters who favored that candidate have their votes transferred to the voters’ second preferences. Any candidate who now has more than the winning threshold is declared elected.
4. This process continues until all of the seats are filled.
However – a vote for single candidate, or only a few, may be wasted if that (or those) candidate(s) either have enough support from others to win a seat – or have so little support that she or he cannot win a seat. For this reason, the best strategy is always for the voter to rank as many candidates as they have an opinion about.
Cambridge, Massachusetts has used STV to elect its city council and school committee since the 1940s. At one time, STV was used by over 20 cities in the United States, including New York City at the time of Mayor LaGuardia.